Blair is recruited by another department to investigate a suspected Soviet agent – a Czech-born woman with whom he once had an affair. But Palfrey believes the department may have hidden motives for requesting Blair's aid.

A former British agent who defected to the Soviet Union makes an unannounced return, threatening to embarrass both countries. Under instructions to silence him, Palfrey decides to up the stakes.

A tell-all book alleges that the British government assassinated an Iranian general in the 1950s and helped topple a regime. Ordered to prevent its publication, Palfrey suspects a cover-up.

A disgruntled former government official believes that double agents still work in the intelligence service—and threatens to tip off the press unless something is done. The Co-Ordinator assigns Palfrey to head him off.

On advice from the CIA, Palfrey surveils an American aerospace engineer suspected of passing the Soviets classified information about an Anglo-American defense project. It looks like the case may unearth the mole, but can Palfrey trust the CIA?

A contact at the Soviet embassy informs the Co-Ordinator that one of her agents is 'playing a double game'. Since she doesn't hold this agent in high regard, the Co-Ordinator tells Palfrey to look into it—but he suspects a set-up.